Evaluating the threshold limit value of acceptable exposure concentration for exposure to bioaerosols in a wastewater treatment plant: Reverse-quantitative microbial risk assessment and sensitivity analysis.

Agitation operations produce numerous pathogenic bioaerosols in WWTPs1. QMRA2 can determine risks of persons exposed to these bioaerosols. However, QMRA framework cannot help stakeholders in immediately deciding whether a risk is intolerable. Thus, evaluating threshold of acceptable exposure concentration is an urgent issue but is still rarely addressed in WWTPs. This study analyzed TLV3 benchmarks of E. coli and S. aureus bioaerosols emitted from a WWTP by reverse-QMRA. Furthermore, variance of input parameters was clarified by sensitivity analysis. Results showed that, under conservative and optimistic estimates, TLV of technicians was 1.52-2.06 and 1.26-1.68 times as large as those of workers, respectively; wearing mask drive TLV up to 1-2 orders of magnitude; TLV of M4 was at most 1.33 and 1.31 times as large as that of RD5, respectively. For sensitivity analysis, removal fraction by equipping PPE enlarge TLV for effortlessly obtaining an acceptable assessment result; exposure time was dominant when without PPE excepting the scenario of technicians exposed to E. coli bioaerosol. This study helps establish threshold guidelines for bioaerosols in WWTPs and contribute innovative perspectives for stakeholders.

Bioaerosols emission characteristics from wastewater treatment aeration tanks and associated health risk exposure assessment during autumn and winter.

Aeration tanks from activated sludge wastewater treatment plants (WWTPs) can release a large amount of bioaerosols that can pose health risks. However, risk characterization of bioaerosols emissions form wastewater treatment plants is currently not systematically carried out and still in its infancy. Therefore, this study investigated emission characteristic of two indicator model bioaerosols Staphylococcus aureus and Escherichia coli, emitted from aeration tanks of a municipal WWTP. Monte Carlo simulation was then used to quantitatively assess microbial risk posed by different aeration modes under optimistic and conservative estimates. Further to this, two different exposure scenarios were considered during 3 days sampling campaign in autumn and winter. Results showed that the bioaerosol concentration from microporous aeration tank (20-262 CFU m-3) was one order of magnitude lower than rotating disc aeration tank. Average aerosolization rate was 7.5 times higher with mechanical aeration mode. Health risks of exposed populations were 0.4 and 9.6 times higher in winter than in autumn for E. coli and S. aureus bioaerosol, respectively. Health risks of staff members were 10 times higher than academic visitors. Interesting results were observed for academic visitors without personal protective equipment (PPE) respectively exposed to S. aureus and E. coli bioaerosol in autumn and winter: while the derived infection risk met the United States Environmental Protection Agency (U.S. EPA) benchmark under optimistic estimation, the disease risk burden was over the World Health Organization (WHO) benchmark under conservative estimation. These revealed that only satisfying one of the two benchmarks didn't mean absolute acceptable health risk. This study could facilitate the development of better understanding of bioaerosol quantitative assessment of risk characterizations and corresponding appropriate risk control strategies for wastewater utilities.

What are the disease burden and its sensitivity analysis of workers exposing to Staphylococcus aureus bioaerosol during warm and cold periods in a wastewater treatment plant?

Biological treatment in wastewater treatment plants releases high amounts of pathogenic bioaerosols. Quantitative microbial risk assessment is a framework commonly used for quantitative risk estimation for occupational exposure scenarios. However, the quantitative contributions of health-risk-estimate inputted parameters remain ambiguous. Therefore, this research aimed to study the disease burden of workers exposed to Staphylococcus aureus bioaerosol during warm and cold periods and strictly quantify the contributions of the inputted parameters by sensitivity analysis on the basis of Monte Carlo simulation. Results showed that the disease health risk burden of workers in the warm period was 1.15-6.11 times higher than that of workers in the cold period. The disease health risk burden of workers without personal protective equipment was 23.83-36.55 times higher than that of workers with personal protective equipment. Sensitivity analysis showed that exposure concentration and aerosol ingestion rate were the first and second predominant factors, respectively; the sensitivity partitioning coefficient of the former was 1.17-1.35 times the value of the latter. In addition, no remarkable differences were revealed in the sensitivity percentage ratio between warm and cold periods. The findings could contribute to the mitigation measures for the management of public health risks.

Quantitative microbial risk assessment and sensitivity analysis for workers exposed to pathogenic bacterial bioaerosols under various aeration modes in two wastewater treatment plants.

Wastewater treatment plants (WWTPs) could emit a large amount of bioaerosols containing pathogenic bacteria. Assessing the health risks of exposure to these bioaerosols by using quantitative microbial risk assessment (QMRA) is important to protect workers in WWTPs. However, the relative impacts of the stochastic input variables on the health risks determined in QMRA remain vague. Hence, this study performed a Monte Carlo simulation-based QMRA case study for workers exposing to S. aureus or E. coli bioaerosols and a sensitivity analysis in two WWTPs with various aeration modes. Results showed that when workers equipped without personal protective equipment (PPE) were exposed to S. aureus or E. coli bioaerosol in the two WWTPs, the annual probability of infection considerably exceeded the U.S. EPA benchmark (≤10E-4 pppy), and the disease burden did not satisfy the WHO benchmark (≤10E-6 DALYs pppy) (except exposure to E. coli bioaerosol for disease health risk burden). Nevertheless, the use of PPE effectively reduced the annual infection health risk to an acceptable level and converted the disease health risk burden to a highly acceptable level. Referring to the sensitivity analysis, the contribution of mechanical aeration modes to the variability of the health risks was absolutely dominated in the WWTPs. On the aeration mode that showed high exposure concentration, the three input exposure parameters (exposure time, aerosol ingestion rate, and breathing rate) had a great impact on health risks. The health risks were also prone to being highly influenced by the various choices of the dose-response model and related parameters. Current research systematically delivered new data and a novel perspective on the sensitivity analysis of QMRA. Then, management decisions could be executed by authorities on the basis of the results of this sensitivity analysis to reduce related occupational health risks of workers in WWTPs.

Highly Effective and Low-Cost MicroRNA Detection with CRISPR-Cas9.

MicroRNAs have been reported as related to multiple diseases and have potential applications in diagnosis and therapeutics. However, detection of miRNAs remains improvable, given their complexity, high cost, and low sensitivity as of currently. In this study, we attempt to build a novel platform that detects miRNAs at low cost and high efficacy. This detection system contains isothermal amplification, detecting and reporting process based on rolling circle amplification, CRISPR-Cas9, and split-horseradish peroxidase techniques. It is able to detect trace amount of miRNAs from samples with mere single-base specificity. Moreover, we demonstrated that such scheme can effectively detect target miRNAs in clinical serum samples and significantly distinguish patients of non-small cell lung cancer from healthy volunteers by detecting the previously reported biomarker: circulating let-7a. As the first to use CRISPR-Cas9 in miRNA detection, this method is a promising approach capable of being applied in screening, diagnosing, and prognosticating of multiple diseases.